Description

The clock_settime() function sets the specified clock, clock_id, to the value specified
by tp. Time values that are between two consecutive non-negative integer multiples
of the resolution of the specified clock are truncated down to the smaller
multiple of the resolution.

The clock_gettime() function returns the current value tp for the specified clock,
clock_id.

The resolution of any clock can be obtained by calling clock_getres(). Clock
resolutions are system-dependent and cannot be set by a process. If the
argument res is not NULL, the resolution of the specified clock is
stored in the location pointed to by res. If res is NULL, the
clock resolution is not returned. If the time argument of clock_settime() is
not a multiple of res, then the value is truncated to a multiple
of res.

A clock may be systemwide (that is, visible to all processes) or
per-process (measuring time that is meaningful only within a process).

A clock_id of CLOCK_REALTIME is defined in <time.h>. This clock represents the
realtime clock for the system. For this clock, the values returned by
clock_gettime() and specified by clock_settime() represent the amount of time (in seconds and
nanoseconds) since the Epoch. Additional clocks may also be supported. The interpretation
of time values for these clocks is unspecified.

A clock_id of CLOCK_HIGHRES represents the non-adjustable, high-resolution clock for the system.
For this clock, the value returned by clock_gettime(3RT) represents the amount of
time (in seconds and nanoseconds) since some arbitrary time in the past;
it is not correlated in any way to the time of day,
and thus is not subject to resetting or drifting by way of
adjtime(2), ntp_adjtime(2), settimeofday(3C), or clock_settime(). The time source for this clock
is the same as that for gethrtime(3C).

Additional clocks may also be supported. The interpretation of time values for
these clocks is unspecified.

Return Values

Upon successful completion, 0 is returned. Otherwise, -1 is returned and
errno is set to indicate the error.

Errors

The clock_settime(), clock_gettime() and clock_getres() functions will fail if:

EINVAL

The clock_id argument does not specify a known clock.

ENOSYS

The functions clock_settime(), clock_gettime(), and clock_getres() are not supported by this implementation.

The clock_settime() function will fail if:

EINVAL

The tp argument to clock_settime() is outside the range for the given clock ID; or the tp argument specified a nanosecond value less than zero or greater than or equal to 1000 million.

The clock_settime() function may fail if:

EPERM

The requesting process does not have the appropriate privilege to set the specified clock.